End-Guadalupian mass extinction and negative carbon isotope excursion at Xiaojiaba, Guangyuan, Sichuan

The end-Paleozoic biotic crisis is characterized by two-phase mass extinctions; the first strike, resulting in a large decline of sessile benthos in shallow marine environments, occurred at the end-Guadalupian time. In order to explore the mechanism of organisms' demise, detailed analyses of depositional facies, fossil record, and carbonate carbon isotopic variations were carried out on a Maokou-Wujiaping boundary succession in northwestern Sichuan, SW China. Our data reveal a negative carbon isotopic excursion across the boundary; the gradual excursion with relatively low amplitude (2.15aEuro degrees) favors a long-term influx of isotopically light C-12 sourced by the Emeishan basalt trap, rather than by rapid releasing of gas hydrate. The temporal coincidence of the beginning of accelerated negative carbon isotopic excursion with onsets of sea-level fall and massive biotic demise suggests a cause-effect link between them. Intensive volcanic activity of the Emeishan trap and sea-level fall could have resulted in detrimental environmental stresses and habitat loss for organisms, particularly for those benthic dwellers, leading to their subsequent massive extinction.